Signaling within the striatum is critical to procedural learning, habit formation, and movement disorders. In this proposal, I seek to identify a function for a novel, striatum-enriched signaling molecule recently discovered in the sponsor's lab, termed CalDAG-GEFI (calcium, diacylglycerol-activated guanine nucleotide exchange factor I, aka RasGRP2). In cultured cells, CalDAG-GEFI directly stimulates the small G protein Rap 1, which activates the extracellular signal regulated kinase (ERK) cascade via B-Raf. Recently, Rap 1, B-Raf and ERK have been shown to be required for learning/memory and long-term potentiation, a putative electrophysiological correlate to memory. Therefore, I propose that CalDAG-GEFI may regulate the ERK pathway to mediate striatal-based learning and memory. To test this hypothesis, I have generated two lines of CalDAG-GEFI knockout mice, one in which expression is disrupted constitutively and another carrying a conditional mutation in CalDAG-GEFI so that expression may be disrupted specifically in the adult striatum. At a systems level, I will measure learning and memory in wild type versus CalDAG-GEFI knockout mice in a variety of learning paradigms, including a striatal-based task, the win-stay T-maze. The sponsor's lab has developed a 4-tetrode head stage to record from ensembles of neurons in the striatum of mice as they undergo training in the T-maze. I will use this technology to assess basal firing activity in the striatum of knockout mice as well as changes in activity that occur during acquisition, over-training and extinction of the T-maze paradigm. In addition, I propose biochemical experiments to test whether CalDAG-GEFI interacts with members of the ERK cascade in the striatum and whether signaling through this cascade is disrupted in CalDAG-GEFI knockout mice.